Reducing the environmental impact of coating compositions, such as that associated with emissions into the air of volatile organics during their application has been an area of ongoing investigation and development in recent years. Accordingly, interest has increased in coating compositions containing low levels of volatile organic compounds (“low VOC coating compositions”).
In certain markets, such as the consumer electronics market, it is desirable to apply protective and decorative coatings to plastic substrates, such as substrates constructed of acrylonitrile butadiene styrene and/or polycarbonate, among other materials. One problem that has been associated with the application of such coatings to these types of substrates, however, is achieving adequate adhesion of the coating to the substrate. In some cases, adequate adhesion is achieved by using solventborne coatings that utilize solvents that chemically “etch” the substrate, thereby causing physical entanglement of the polymer chains of the substrate with the polymer chains in the coating. Such coating compositions, however, are incompatible with the desire to achieve environmentally friendly, low VOC coating compositions.
Other properties desirable in coating compositions suitable for application to plastic substrates are humidity resistance and hardness. Humidity resistance is a measure of the ability of a coating to remain intact and unblemished after exposure to water, while harder coatings are more resistant to scratching and marring. It would be desirable to provide waterborne coating compositions suitable for application to plastic substrates, which can exhibit good adhesion properties to such substrates, while having sufficient humidity resistance and hardness properties.